The disclosure relates to an electrohydraulic system for use under water, in particular at great water depths. The system comprises a vessel which has an interior space which is provided for forming a volume that is closed off in relation to the environment and is provided for receiving a hydraulic fluid, and a compensation piston, so as to pressurize the hydraulic fluid in the interior space to at least approximately that pressure that prevails in the environment. The system furthermore comprises a hydrostatic machine that is operable at least as a pump, and an electro-machine that is mechanically coupled to the hydrostatic machine and operates as an electric motor for operating the hydrostatic machine as a pump, and a hydro-cylinder, of which the interior is subdivided into a cylinder chamber proximal to the piston rod, and into a cylinder chamber distal to the piston rod by way of a piston to which a piston rod is connected, wherein in order for the piston rod to be moved in a first direction, in particular in order to deploy the piston rod, pressurized fluid is infeedable from the hydrostatic machine operating as a pump to a first cylinder chamber, in particular to the cylinder chamber distal to the piston rod.
Electrohydraulic systems of this type are used in the context of crude oil and natural gas exploration, of mining, of natural-science research, or of infrastructure projects above all for moving an element under water at water depths down to several thousand meters. In this way, process valves by way of which the volumetric flow of the medium to be conveyed may be regulated or shut off are located at great depths of the ocean in the case of crude-oil or natural-gas well installations, for example.
An electrohydraulic system having the features listed above is known from U.S. Pat. No. 3,933,338, for example. This system comprises a hydro-cylinder of which the cylinder housing sits on the housing of a process valve, and which comprises a piston and a piston rod that unilaterally protrudes from the piston and by way of which a process-valve stem of the process valve may be moved. The piston subdivides the interior of the cylinder housing into a cylinder space distal to the piston rod, and into a cylinder space proximal to the piston rod. A helical spring which impinges the piston in the sense of closing the process valve is accommodated in the cylinder space proximal to the piston rod. The known system furthermore comprises a vessel of the interior space that is filled with a pressurized fluid at one point is separated from the environment by a movable compensation piston. The compensation piston on a first face is impinged by the pressure in the interior space of the vessel, and on a second face which is of identical size to the first face and is directed so as to oppose the latter is impinged by the ambient pressure such that the same pressure prevails in the interior space as in the environment. The cylinder space proximal to the piston rod is in permanent fluidic communication with the interior space of the vessel. The cylinder space distal to the piston rod, depending on the position of a hydraulic valve, is either connected to a pump or to the interior space of the vessel and to the cylinder space proximal to the piston rod. Thus, pressurized fluid may be conveyed by the pump into the cylinder space distal to the piston rod in the one position of the valve, in order for the piston rod to be deployed and for the process valve to be opened. Upon switching of the hydraulic valve, the piston rod is retracted by a spring force such that the process valve closes.
The disclosure is based on the object of achieving a compact electrohydraulic system which may be installed in existing as well as new equipment, on the one hand, and to enable a process valve of compact construction including an electrohydraulic system, on the other hand.